The present invention relates to an opening arrangement for packing containers of the type which are used for liquid contents and which are manufactured wholly or partly from a packing laminate comprising layers of fibrous carrier material and thermoplastics, this opening arrangement comprising a prepared pouring opening and a tear-off cover strip applied over the same.
The invention also relates to a method for the manufacture of an opening arrangement of this type.
Packing containers of the non-returnable type are used to an increasing extent for the packaging of liquid foodstuffs such as milk, juice and wine. In general the packing containers are formed from a prefabricated, laminated packing material which comprises a carrier layer of fibrous material, e.g. paper, which at least on one, and usually on both, rides is covered with liquid-tight layers of thin thermoplastic material, e.g. polyethylene. Packing laminate of this type is of a total thickness of approx. 0.4 mm and is therefore very flexible and apt to be converted by folding and heat-sealing to individual packing containers of the desired, e.g. parallelepipedic shape. The packing containers are usually also provided with some form of opening arrangement, e.g. a tearing or cutting indication or a tear-off cover strip (so-called pull-tab) which is sealed in a liquid-tight manner over a pouring opening in the packing container wall.
An opening arrangement of the type which comprises a pouring opening prepunched into the material and a tear-off cover strip applied over this in a liquid-tight manner has many advantages in that it is easy to handle, apt to be applied to the packing material beforehand, that is to say while the same is still in form of a web prior to conversion to individual packing containers, and low in cost. In the packaging of liquid contents it has to be ensured, however, that the edge of the packing laminate exposed on punching the holes is protected in a suitable manner from the contents, since otherwise these will be absorbed by the fibrous carrier layer so that the laminate is loosened up and acquires inferior strength and appearance. To prevent absorption it is customary, therefore, in this type of packing container to apply, beside the outer cover strip, also an inside protective layer, e.g. of thermoplastic material, which is present on the side of the packing laminate facing towards the contents and covers the pouring opening as well as the area around the same. The cover layer is sealed to the cover strip via the pouring opening so that the cover layer breaks in connection with the tearing off of the cover strip thus making possible the pouring out of the contents through the pouring opening. However, as a result the cut edge of the laminate previously covered is also exposed so that a certain absorption will take place when the contents during pouring come into contact with the cut edge. This is undesirable for hygienic and aesthetic reasons.
In the packaging of sterile contents, e.g. sterile milk, aseptic packages are used which, by and large, are of the same design and formation as the packing container described above. However, the packing laminate here comprises usually one or more further layers in order to improve the gas-tightness of the laminate. As a gas barrier in general a metal foil, e.g. an aluminium foil, is used which is applied to the inside of the laminate and is covered by a further layer of thermoplastic material, e.g. polyethylene. Here it is particularly important to avoid any contact between the metal foil and the contents, not only during the storage of the contents in the closed packing container but also during the pouring out of the contents and storage of remaining contents in the opened package. This applies in particular to acid types of contents, e.g. juice and wine, since contact between these contents and metal foil brings about a chemical change which affects the flavour of the product. This is true not only during the storage of the contents in the packing container before the opening of the same but also on pouring out, since any residues of contents which "get stuck" around the pouring opening, after a prolonged contact with the metal foil, may drop back into the package or in each case are carried along in subsequent pourings out of the contents.
Previous solutions designed to overcome the aforementioned problem in aseptic packing containers with prepunched pouring opening and tear-off cover strip have been relatively complicated and included an internal cover layer in the form of a laminated strip which not only should prevent any contact of the contents with the cut edge of the pouring opening, but also ensure that a satisfactory gas barrier is formed between the contents and the said cut edge, since otherwise a gas exchange with the surrounding atmosphere may ensue via the cut edge and the outer thermoplastic layer of the packing laminate. The gas barrier layer (metal foil) of the laminate is situated on the inside of the laminate. A known gas-tight and liquid-tight internal strip thus comprises a layer of polyvinylidene chloride serving as a gas barrier which via intermediate sealing layers of EVA (ethylenevinyl alcohol) is coated on both sides with polyethylene. Such a strip is relatively expensive and has been found, moreover, to be subject to two disadvantages, namely on the one hand that the different strip layers will delaminate from one another on opening of the packing container so that only certain layers join the cover strip when the latter is torn off, which means that remaining layers hinder the pouring out of the contents, on the other hand that very small cracks or holes (so-called pinholes) are formed opposite the cut edge of the packing laminate on application of the internal layer or strip. This appears to be due to the strip in this region being subjected to a stretching at the same time as it is heated to be sealed to the internal thermoplastic layer of the laminate as well as to the external cover strip via the pouring opening.
It is an object of the present invention to provide an opening arrangement of the aforementioned type which is suitable also for aseptic packages and which is not subject to the disadvantages which have been described in connection with known opening arrangements.
It is a further object of the present invention to provide an opening arrangement where the edge of the pouring opening is protected in such a manner that high gas and liquid-tightness is obtained without any internal covering layer having to be used.
It is a further object of the present invention to provide an opening arrangement which meets the extremely high demands which are made on packing containers for sterile products.
These and other objects have been achieved in accordance with the invention in that an opening arrangement has been given the characteristic that the edge of the carrier layer material facing towards the pouring opening is covered by means of thermoplastic layers present on both sides of the carrier layer which meet each other and are joined in a liquid-tight manner in a seal extending around the pouring opening.
By the design of the opening arrangement in accordance with the invention it becomes possible to guarantee a high liquid-tightness and to prevent the contents from being absorbed into the carrier layer of the packing laminate in the region around the pouring opening, at the same time as the opening arrangement, when it is used on a packing laminate with gas barrier layer, gives a high gastightness and prevents contact between the contents and the gas barrier layer.
It is a further object of the present invention to provide a method for the manufacture of the abovementioned opening arrangement.
It is a further object of the present invention to provide a method of manufacture which makes it possible in a simple and effective manner to provide a packing laminate with liquid-tight and gas-tight opening arrangements, this method being suitable to be used in the manufacture on very high speed machines.
These and other objects have been achieved in accordance with the invention in that a method for the manufacture of an opening arrangement for packing containers of the type which are used for liquid contents and which are manufactured wholly or partly from a packing laminate comprising layers of fibrous carrier material and thermoplastics, this opening arrangement comprising a prepared pouring opening and a tear-off cover strip applied over the same, has been given the characteristic that the carrier layer of the packing material is provided with a hole of a predetermined shape and size, whereupon the carrier layer is coated with the required layers of gas-tight or liquid-tight material so that the carrier layer receives at least one layer of thermoplastic material on each side, these layers being made to form a seal with each other through the application of heat and pressure, whereupon a second hole is cut out at the same place as the first mentioned hole, this second hole, however, being of a slightly smaller size so that a pouring opening is formed whose extent is limited by remaining parts of the external thermoplastic layers of the laminate sealed to each other, whereupon an external cover strip is sealed, so that it can be torn off, to the outside of the packing laminate over the pouring opening.
The method in accordance with the invention permits the manufacture of opening arrangements containing a pouring opening and a cover strip where the cut edge of the packing laminate extending around the pouring opening is effectively protected from the contents.